1. Field of the Invention
The present invention relates to, for example, a signal processing apparatus and method for performing signal processing on an input signal, amplifying a power supply voltage in accordance with the processed signal, and outputting the amplified power supply voltage as an output signal.
2. Description of Related Art
FIG. 14 is a block diagram of a related art digital amplifier system. In FIG. 14, an amplifier signal processing block 141 performs predetermined signal processing on an amplifier input signal 145, and a delay device 2 delays the processed signal by the amount of delay occurring in the digital amplifier system, in order to adjust the output timing of an amplifier power block 143. Then, a power source block 144 outputs a constant power supply voltage to the amplifier power block 143 under feedback control 147, and the amplifier power block 143 amplifies the power supply voltage in accordance with the level of the delayed signal and outputs an amplifier output signal 146.
The amplifier power block 143 of the digital amplifier system cuts out the power supply voltage supplied from the power source block 144 by means of the switching operation of its power MOS (metal oxide semiconductor). The voltage cut out by the power MOS is desirably a stable constant voltage, and if a voltage variation occurs, the voltage variation directly influences an audio output signal such as the amplifier output signal 13 and produces distortion of the audio output signal. In general, to suppress the voltage variation, the output of the power source block 144 is fed back (as indicated at 147) to the power source block 144 itself so as to suppress a variation of the output voltage.
FIGS. 12A to 12C are graphs showing waveform distortions due to a power supply voltage variation, and FIG. 12A shows a voltage applied to the power MOS (after correction), FIG. 1-2B shows an ideal switching pulse of the power MOS, and FIG. 13C shows a switching pulse of the power MOS during the power supply voltage variation.
If the level of the signal delayed by the delay device 142 increases and a lowering variation occurs in the power supply voltage supplied from the power source block 144, the voltage applied to the power MOS shown in FIG. 14A (before correction) lowers from a constant voltage by the amount of the variation of the power supply voltage. As a result, the power MOS switching pulse during the power supply voltage variation shown in FIG. 12C lowers by the amount of the variation of the power supply voltage compared to the ideal power MOS switching pulse shown in FIG. 12B.
An audio switching power source has been proposed which is constructed to determine a pulse modulated signal for determining a direct-current output value of an AC-DC conversion section by means of a pulse control section on the bias of the amplitude value of a sequentially inputted digital input signal, the audio switching power source being operative to correct the direct current output voltage at the same timing as an increase of the amplitude of the digital input signal by outputting an audio signal which is power-amplified by a digital power amplification section after having delaying the digital input signal (refer to Japanese Patent Application Publication Laid-Open Number Hei 9-148851).
A power supply circuit for a power amplifier has also been proposed which varies a power supply voltage to be supplied to a power amplification device of the power amplifier, in accordance with the envelope of a signal level based on an input signal (refer to Japanese Patent Application Publication Laid-Open Number Sho 57-11507). Furthermore, a multi-signal amplifier is known which varies a bias voltage to be supplied to a power amplification circuit, in accordance with the number of input signals (refer to Japanese Patent Application Publication Laid-Open Number Hei 3-250805). In addition, a solid-state power amplifier has also heretofore been known which detects an input and an output and performs dynamic adjustment of an operation point for dynamically adjusting a direct-current bias to be supplied to the amplifier (refer to Japanese Patent Application Publication Laid-Open Number Hei 4-262608).